Tumelo geology.
Tumelo is to the north of the Smithfield Ridge on the northeastern edge of the Springs-Witbank coalfield. The area is part of the Karoo basin with stratigraphy similar to that of other ECC operations, Dorstfontein and Forzando with subtle location-induced differences.

Six coal seams are developed in the area, named from the base up as S1, S2, S4L, S4U, S4A and S5. S1 is very thin, being only developed in the deepest part of the palaeo-valley. The thickest average seam is the S2 (0.5m to 5.3m), developed mainly in a palaeo-valley where it is either thin or absent over the adjacent palaeo-ridges. S2 has been exploited since Tumelo production started in 2009. S4L is the most continuous and secondthickest seam while S4U is thin and has mostly been eroded. S4A is thin and patchily developed and S5 is only present in a topographically high area in the south east. The only economically exploitable seam is S2.

Late Jurassic dolerite sills and dykes occur in the Tumelo area. The intrusions resulted in displacement of the various seams and devolatilisation of extensive areas of coal. The geological complexity and associated challenges are proactively managed by extensive infill drilling, downhole wireline logging for better contact definition and seam correlation as well as surface mapping, particularly of basement outcrops. This information is captured in a structural model, together with potential risks captured in a GIS-based risk and opportunity domain analysis (RODA), allowing for a more integrated approach to risk management.

A 2002 feasibility study confirmed the presence of economic coal reserves. First coal was recorded in 2009, with Tumelo exploiting S2 using bord-and pillar. Mining was outsourced to SBS Mining Proprietary Limited, a mining contractor.

Using one continuous miner, the mine produced some 700kt ROM at its peak. Initially, this was custom washed for an export product at the Shanduka (Glencore-owned) Koornfontein mine washing plant, but would later be carted to Forzando North and washed for a 5 800kcal/kg export product.